1. Field of the Invention
The present invention relates to a distal end part of an endoscope. More particularly, the present invention pertains to a transparent cover that is provided at the distal end of the insert part of an endoscope to cover the respective surfaces of an illuminating window and a viewing window.
2. Description of the Related Art
A viewing window and an illuminating window are disposed side by side at the distal end of the insert part of an endoscope. The surfaces of these windows must be covered with a transparent cover so that water or other external matter will not enter the endoscope. The transparent cover has heretofore been provided independently for each of the surfaces of the viewing and illuminating windows.
Recently, the possibility that bacteria and viruses will be transferred from one patient to another through an endoscope has attracted attention and there has been an increasing need to prevent such a problem effectively and reliably.
One such effective means is to use an endoscope with its insert part being covered with a watertight sheath which enables the insert part to be removably inserted thereinto and replace the sheath with a new one after the use. In this case, that portion of the sheath which covers the surfaces of the viewing and illuminating windows must be transparent.
However, when the surfaces of the two windows are covered with a single continuous transparent cover, problems arise. For example, as shown in FIG. 14, a part of the illuminating light that is emitted from an illuminating window 101 enters a viewing window 103 after being repeatedly reflected within a transparent cover 102, thus causing a ghost or flare to appear in the observation field of view. Since the illuminating light that is emitted from the illuminating window of an endoscope is considerably bright, the ghost or flare thus produced is so intense that the endoscope cannot practically be used.
Theoretically, it is possible to form a cover in which those portions thereof which cover the respective surfaces of the viewing and illuminating windows are transparent, while the portion thereof which extends therebetween is opaque. However, it will be highly costly to produce such a cover that only those portions thereof which face the respective surfaces of the two windows are transparent independently of each other because of the endoscope structure in which the two windows, each having a diameter of about several millimeters, are disposed in close proximity to each other. In addition, the transparent portions of the cover may be displaced from the respective windows during use.
In the case where transparent covers are provided for the respective surfaces of the two windows as in the common practice, a light shielding black adhesive or the like must be filled in the top portion of a partition wall that partitions off the two windows from each other so that illuminating light will not enter the viewing window through the top portion of the partition wall. In this case, however, when a drop of water or the like is caught on the adhesive-filled portion, the observation field of view is disturbed. The adhesive may come off during repetitive use and, if a drop of water is attached to the exposed top portion of the partition wall, illuminating light enters the viewing window through the water drop that functions as a lens, thus causing a ghost or flare to appear in the observation field of view.